Twenty-four US states have HIV-specific criminal laws that require persons living with HIV to disclose their positive serostatus to prospective sex partners. Moreover, lawmakers in US states without these laws regularly propose such legislation. Although the presumptive purpose of the laws is to increase serostatus disclosure to sexual partners (with the assumption that informed partners will abstain or practice safer sex), little is known about their effectiveness. Even less is known about the potential negative effects of the laws, which range from discouraging HIV testing and undermining central HIV prevention messages to fostering increased HIV-related stigma and deterring (rather than promoting) seropositive status disclosure by increasing the potential negative consequences of disclosing one's HIV-positive status. US HIV disclosure laws also take several different forms, which introduces further variability and additional statute-specific concerns. Only one empirical study has directly assessed the effects of US HIV disclosure laws on persons living with HIV. The study was conducted in Michigan, a state with an HIV disclosure law, by the PI of the proposed project. No direct empirical studies have examined the impact of the laws on HIV-negative or serostatus unknown persons at risk for HIV infection. The proposed project will expand our successful preliminary study on HIV disclosure laws. We will survey statewide samples of 400 persons living with HIV and 200 persons at risk for the infection in each of four US states, three with different versions of HIV disclosure laws and one with no law. Results from the study will determine positive and negative effects of the laws on HIV-positive and HIV- negative, at-risk individuals. Comparison of states with differing laws has the further potential to determine which aspects of criminal disclosure laws are useful in terms of promoting the intended outcome (safer sex behavior within sero-discordant couples, or sexual abstinence) and which aspects have unintended negative consequences. The results of the study will inform HIV-related legislation, which is often drafted without the benefit of scientific evidence. Results will also inform policy discussions on the role of the criminal law in disease containment efforts.